The present invention relates to a chain block and particularly to improvements in a construction for attaching the load-free end link of a load chain.
The chain block which has heretofore been in general use, as shown in FIG. 1, comprises a load sprocket wheel 4 rotatably supported between a pair of lateral plates 2 and 3 having a suspension hook 1 attached thereto, and a load chain 5 entrained around said load sprocket wheel 4, said load chain having a load-free end link 5a attached to the lateral plates by a pin 6 extending therethrough, a load hook 7 connected to the load end link 5b of said load chain, a hand-operated sprocket wheel 9 which is rotated by a hand-operated chain 8 to rotate the load sprocket wheel 4 through a brake mechanism 10 and a speed reducing gear mechanism 11 to thereby lift and lower load hook 7 connected to the load chain 5. Since the load-free end link 5a of the load chain 5 is locked to the attaching pin 6, the lowering of the load chain 5 to the fullest extent will result in the load chain 5 being stretched between the pin 6 and the load sprocket wheel 4, preventing any further lowering. In this connection, it often occurs that not knowing that the lowering limit has already been reached, the operator further pulls the hand-operated chain 8 strongly in the lowering direction. In such cases, the suspended load hooked by the load hook 5 is transmitted through the load-free end link 5a of the load chain 5 to act concentratedly on the middle portion of the attaching pin 6 between the lateral plates 6 to exert a heavy bending moment on the attaching pin 6. This sometimes breaks the attaching pin 6, releasing the suspended load to fall downward to injure or even kill the operator or other persons. Guide rollers 12 for the load chain 5 are disposed on both sides of the load sprocket wheel 4 and are strongly pressed by the load chain 5, so that it is necessary for the guide rollers 12 and the support structure therefor to have a strength several times as high as the value usually required by the guide rollers themselves. The load chain 5 strongly pressing the guide rollers 12 is liable to come in abnormal contact therewith and break, causing an accident.
On the other hand, devices intended to eliminate the above-described drawbacks are known, as found, for example, in Japanese Utility Model Publication Nos. 34392/1973 and 34391/1973. According to these devices, the load-free end link of the load chain is locked to the front end of a lever-shaped support which is pivotally mounted at one end thereof between a pair of lateral plates so that when the load chain is lowered to the fullest extent, the lever-shaped support contacts a guide roller to stretch the load chain without bringing the load-free portion of the load chain into contact with said guide roller, and any further lowering of the load chain is prevented by the pressure contact of said lever-shaped support with the guide roller. Therefore, since the load-free end portion of the load chain is not subjected to an excessive load which would be exerted if it contacts the guide roller, the attaching strength is increased. However, the lever-shaped support exerts the full load acting on the load chain on the guide roller it contacts. As a result, it is necessary for the guide roller and the support structure therefor to have a strength several times as high as the value heretofore required.